Polyaspartic acid is a peptide chain in which amide linkages extend the chain. In the thermal polymerization of aspartic acid, the stereochemistry of the aspartic acid is racemized and the formation of both .alpha. and .beta. carboxylic acid groups have the ability to react to form such amide bonds. Such materials have been used for fertilizers and scale inhibition agents. They are particularly useful for the prevention of scale deposition in boiler water, reverse osmosis membranes, detergents and as inhibitors of dental tartar and plaque formation (tartar barrier agents). These materials are readily biodegradable. Methods for the preparation of polyaspartic acid have been developed (see U.S. Pat. Nos. 5,057,597 and 4,839,461 and U.S. patent application Ser. No. 07/882,919, filed May 14, 1992, Louis L. Wood, and U.S. patent application Ser. No. 07/926,242, filed Aug. 7, 1992, Louis L. Wood).
Biodegradability, calcium ion exchange ability and the disruption of calcium salt crystal structure are important properties of materials used in the prevention of scale deposition in boiler water, on reverse osmosis membranes, in detergent use and as inhibitors of dental tartar and plaque formation (tartar barrier agents). We searched for economically useful materials, having a greater retention on the object wherein inhibition of scale deposition is desired. Other desirable properties were greater stability to biodegradation in addition to intrinsic value for the prevention of scale deposition in boiler water, on reverse osmosis membranes, during detergent use and as inhibitors of dental tartar and plaque formation (tartar barrier agents). We have found that the addition of polycarboxylic acids in the thermal polymerization of maleic acid or aspartic acid produced novel and highly effective copolymers which possessed these properties.